Smelting of iron and steel



Aug. 14, 1951 A. G. E. ROBIETTE SMELTING OF IRON AND STEEL Filed Nov. 25, 1947 11 ,Hal.

Patented Aug. 14, 1951 "UN l TED .ES PATEN T T FZF ICE 12564-3233 ISMELTINGTUF monann'isrssr. -fllfred Gorlion Evans Robiette; London, unease, a'ssignor:to JohnMiles and-*Partners (London) L-Li-mited, London, 1 England, "a British company 'Applica'tionNovcmber 25, 1947,Serial No. 787,989 In Great Britain December-'18, I946 2 Claims.

I The present invention relates to the manufacture of iron and steel.

In the more usual presenteday processes for manufacturing iron and steel, a ,goodgrade of coking coal is coked in coke ovens, the gas so produced being mixed-with*blast"furnaceigas 'and used in the steelworks, whilstthe coke is used=as fuel in a shaft furnace -such--as -a blastfurnaca.

The coke for the blast furnace must be mechanically strong, resistant-to abrasion and yet must be readily combustible. "This is dueto the fact that the blast furnace has'a' high stackj-tlie total height being of-the orderof "100 ft.,"sothat the coke must be'able to-re'sist the superimposed load of the charge until it is burnt at the'tuyeres, and must also resist abrasion in its descent in the shaft. Otherwise, if the coke .disintegrates, the furnace becomes clogged and does not allow of th free passageof'gas,

' The coking coal reserves of the 'woildlare rrapidly diminishing, and 'insome countriesthe end of these reserves for the production of iron and steel is in sight. It is evident that if the height of the shaft could be substantially reduced then a much weaker fuel can be employed, even possibly a non-coking coal and even anthracite or lignite.

Hitherto such a reduction in the height of the furnace has been possible only if electricity is available in bulk at a low rate, since electricity can then replace fuel as a source of heat, and only approximately 33 to 40% of the weight of carbon is needed as compared with a normal blast furnace.

The usual blast furnace is high to allow of heat transfer from the large volume of gases produced from the combustion of the coke with air and also to get some fuel reduction of the ore in the blast furnace stack.

If oxygen or gas containing a high proportion of oxygen, say over 70% oxygen is used, then the volume of gas produced is considerably reduced. For instance, if pure oxygen is used then only approximately one-fifth of the gas is required. If pro-reduction in the shaft is disregarded then the height of the stack need only be about onefifth of that required in a blast furnace.

In a blast furnace plant also part of the calorific value of the ensuing gas is used to pre-heat the air so as to improve the thermal efliciency.

Oxygen enriched blast has been used in a blast furnace of normal height but it has been found that when the proportion of oxygen rises to about 30% to 40%, the life of the refractories is considerably reduced.

It is an object of the present invention to reducethe quantity'of cokenecessary'for the operation of a blast furnace, without reducing "the output of iron from-the furnace.

"With this end in view, and in accordance with the invention, there isprovided a process-'forthe smelting of iron-containing oresQwhere'in the o'r-e, carbonaceous material and limeare charged into a low shaft furnace the'internal height of which is less than its diameter and into whichis blown, at a pressure of not lesstha'n 50 lbspersquare inch, "a fiuid containing not less than of oxygen.

In the normal blast furnace air'pressures us'ed rangefrom dlbspto 25 lbs. per squareinch, an average being approximately 18 lbs. per square inch. Also ina'fZO ftfhearth diameterblast 'furnace the height "of the stack is "of the orde'r' of feet and such a furnace,'operating on-iro'nores containing say 60% Fe., would produceapproximately 800 tons er pigiron per 24 hours. In a typical "plant in accordance with "the present "invention the diameter of a hearth would be 30 ft. and the effective height of shaft would be about 20 feet whilst the oxygen or oxygen-rich gas pressure would be 90 to lbs. per square inch.

The injection of the gas at this high pressure permits of the use of the adiabatic expansion to provide a cooling efiect in and around the area near the tuyeres, whilst the increased velocity forces the area of maximum temperature towards the centre of the furnace.

A preferred way of carrying out the invention will now be described with reference to the accompanying diagrammatic drawings in which Figure 1 is a sectional elevation of a low shaft furnace and Figure 2 is a flow diagram illustrating the process.

The furnace In illustrated is of larger internal diameter than its height. Thus its internal height, measured at A, may be about 20 feet and its internal diameter, measured at B, about 30 feet. It is formed with a tap hole I l, and tuyeres I2, I3, etc. arranged at equal intervals around its cylindrical wall M. The tuyres are about 4 or 5 feet above the tap hole and each is of convergentdivergent shape, or so-called Venturi shape, to give a rapid adiabatic expansion of the oxygen injected therethrough into the furnace. The furnace is also provided with a take-01f l5 for the reducing gases, mostly carbon monoxide and hydrogen, evolved in the furnace, and with charging chutes such as l6 and I! through which iron ore, coke and lime can be uniformly charged into the furnace.

The manner in which the furnace is operated is illustrated in Figure 2. Ore to be smelted is first pro-reduced in a pre-reducer [8 with the aid of the reducing gases collected from the furnace H1. The partially reduced ore is then skipped to, and charged into, the furnace for smelting.

An oxygen-containing fluid is injected into the furnace through the tuyeres I Z and I3 and smelted iron is tapped periodically from the tap hole fl l.

The fluid may be liquid or gaseous and preferably contains over 70% of oxygen whilst the pressure at which it is injected into the furnace is not less than 50 lbs. per square inch and preferably is of the order of 90 to 100 lbs. per square inch.

The gas issuing from the furnace contains little or no nitrogen and contains up to 70% carbon monoxide with a variable hydrogen content, depending upon the hydrogen content of the coal or coke. This gas has a high reducing value and therefore, as described, can be used to pre-reduce part or all of the iron ore before charging into the furnace. This gas is not required to preheat the blast as it is in normal blast furnace practice and there is no disadvantage in lowering its calorific value by allowing part or all of it to pre-reduce the charge.

If cheap power is available, the oxygen can be made by the electrolysis of water and the hydrogen so produced can be used for pre-reduction of the charge.

Alternatively, part of the oxygen can be made by fractional distillation of liquid air and/ or by the electrolysis of water, the nitrogen and hydrogen so produced being used for the synthesis of ammonia and the production of fertilisers con= taining ammonia as a base.

I claim:

1. A process of smelting iron-containing ores, 4

wherein the ore, carbonaceous fuel and lime are charged into a low shaft furnace the internal height of which is less than any of its internal linear dimensions measured at the tuyere zone in a horizontal plane, and into which furnace is blown, at a pressure of not less than lbs. per square inch, a gaseous fluid containing by volume or more of oxygen.

2. A process of smelting iron-containing ores, wherein the ore, carbonaceous fuel and lime are charged into a low shaft furnace the internal height of which is less than any of its internal linear dimensions measured at the tuyre zone in a horizontal plane, and into which furnace is blown, at a pressure of not less than 50 lbs. per square inch, oxygen-enriched air containing by volume 70% or more of oxygen.

ALFRED GORDON EVANS ROBIETTE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 677 Alger Mar. 29, 1859 43,274 Raschette June 21, 1864 1,021,096 Haggenmiller Mar. 26, 1912 1,283,500 Gray Nov. 5, 1918 1,629,045 Parker May 17, 1927 1,759,559 Job May 20, 1930 1,824,960 Lawaczeck Sept. 29, 1931 1,830,683 Wagner Nov. 3, 1931 1,945,341 Brassert Jan. 30, 1934 2,035,550 Karwat Mar. 31, 1936 2,079,019 Karwat May 7, 1937 OTHER REFERENCES Clements: Blast Furnace Practice, vol. I, pages 464 and 465; and Blast Furnace Practice, vol II, page 297. Edited by Clements, published in 1929 by Ernest Benn Limited, London, England. 

1. A PROCESS OF SMELTING IRON-CONTAINING ORES, WHEREIN THE ORE, CARBONACEOUS FUEL AND LIME ARE CHARGED INTO A LOW SHAFT FURNACE THE INTERNAL HEIGHT OF WHICH IS LESS THAN ANY OF ITS INTERNAL LINEAR DIMENSIONS MEASURED AT THE TUYERE ZONE IN A HORIZONTAL PLANE, AND INTO WHICH FURNACE IS BLOWN, AT A PRESSURE OF NOT LESS THAN 50 LBS. PER SQUARE INCH, A GASEOUS FLUID CONTAINING BY VOLUME 70% OR MORE OF OXYGEN. 